The Present Disclosure relates, generally, to cable interconnection systems, and, more particularly, to bypass cable interconnection systems for transmitting high speed signals at low losses from chips or processors to backplanes.
Conventional cable interconnection systems are found in electronic devices such as routers, servers and the like, and are used to form signal transmission lines between a primary chip member mounted on a printed circuit board of the device, such as an ASIC, and a connector mounted to the circuit board. The transmission line typically takes the form of a plurality of conductive traces that are etched, or otherwise formed, on or as part of the printed circuit board. These traces extend between the chip member and a connector that provides a connection between one or more external plug connectors and the chip member. Circuit boards are usually formed from a material known as FR-4, which is inexpensive. However, FR-4 is known to promote losses in high speed signal transmission lines, and these losses make it undesirable to utilize FR-4 material for high speed applications of about 10 Gbps and greater. This drop off begins at 6 GBps and increases as the data rate increases.
Custom materials for circuit boards are available that reduce such losses, but the prices of these materials severely increase the cost of the circuit board and, consequently, the electronic devices in which they are used. Additionally, when traces are used to form the signal transmission line, the overall length of the transmission line typically may well exceed 10 inches in length. These long lengths require that the signals traveling through the transmission line be amplified and repeated, thereby increasing the cost of the circuit board, and complicating the design inasmuch as additional board space is needed to accommodate these amplifiers and repeaters. In addition, the routing of the traces of such a transmission line in the FR-4 material may require multiple turns. These turns and the transitions that occur at terminations affect the integrity of the signals transmitted thereby. It then becomes difficult to route transmission line traces in a manner to achieve a consistent impedance and a low signal loss therethough.
It therefore becomes difficult to adequately design signal transmission lines in circuit boards, or backplanes, to meet the crosstalk and loss requirements needed for high speed applications. It is desirable to use economical board materials such as FR4, but the performance of FR4 falls off dramatically as the data rate approaches 10 Gbps, driving designers to use more expensive board materials and increasing the overall cost of the device in which the circuit board is used. Accordingly, the Present Disclosure is therefore directed to a high speed, bypass cable assembly that defines a transmission line for transmitting high speed signals, at 10 GBps and greater which removes the transmission line from the body of the circuit board or backplane, and which has low loss characteristics.